1. Field of the Invention
This invention relates generally to the field of temperature measurement in electronics and computer systems, and, more particularly, to the design of temperature measurement devices to obtain accurate temperature readings for controlling the rotational speed of cooling fans.
2. Description of the Related Art
Many digital systems, especially those that include high-performance, high-speed circuits, are prone to operational variances due to temperature effects. Devices that monitor temperature and voltage are often included as part of such systems in order to maintain the integrity of the system components. Personal computers (PC), signal processors and high-speed graphics adapters, among others, typically benefit from such temperature monitoring circuits. For example, a central processor unit (CPU) that typically “runs hot” as its operating temperature reaches high levels may require a temperature sensor in the PC to insure that it doesn't malfunction or break due to thermal problems. Accurate temperature measurement of processors is therefore necessary when using high performance, high current processors in PCs and/or servers.
Often, integrated circuit (IC) solutions designed to measure temperature in a system will monitor the voltage across one or more PN-junctions, for example a diode or multiple diodes at different current densities to extract a temperature value. Temperature-to-digital conversion for IC-based temperature measuring solutions is often accomplished by measuring a difference in voltage across the terminals of a diode when different current densities are forced through the PN junctions of the diode. The resulting change (ΔVBE) in the base-emitter voltage (VBE) between the diodes is generally proportional to temperature.
Some IC manufacturers began incorporating temperature monitoring and the monitoring of other possible environmental variables within the ICs themselves, oftentimes providing measurement readings to other system components. Those other system components would then typically use these readings to control selected environment variables through a variety of means. One example of such built-in monitoring is Intel Corporation's PECI (Platform Environment Control Interface), which includes a digital bus designed, among others things, to carry Intel CPU temperature readings to an environmental monitor or fan controller.
Fans are often used to evacuate warm air from enclosures in which electronic systems are contained. For example, most computer systems include one or more cooling fans to aid in circulating the air inside the enclosures and for maintaining the temperature inside the enclosures within an acceptable range. The increased airflow provided by fans typically aids in eliminating waste heat that may otherwise build up and adversely affect system operation. Employing cooling fans is especially helpful in ensuring proper operation for CPUs with relatively high operating temperatures.
Control of fans in a system typically involves a fan control unit executing a fan control algorithm. A fan control algorithm may determine the method for controlling one or more fans that are configured to evacuate warm air from a system enclosure. For example, the fan control algorithm may specify that a fan's speed should be increased or decreased dependent upon a detected temperature, which in case of processor cooling could mean the processor temperature. Such control algorithms may also involve turning off a fan if the temperature is deemed cool enough to do so. For detecting the temperature of a processor, a temperature sensor may provide to the fan control unit a signal indicative of the current temperature of the processor.
Because a fan operating at high speed can typically be noisy, it is generally desirable to run the fan as slowly as possible, while maintaining the processor temperature in a safe zone. An accurate temperature reading is therefore necessary to make sure the fan cooling is effective. However, it may be difficult to obtain accurate measurements using remote temperature readings. For example, accuracy can be a problem with Intel Corporation's PECI bus. Periodically, PECI readings may fail without an error indication, returning temperatures that diverge widely from the correct temperature. More specifically, one issue with PECI is that isolated temperature readings may be very much larger or smaller than the actual temperature.
There are at least a couple of ways in which the inaccuracy of temperature measurements for fan controllers has been addressed. One common method is to take the arithmetic mean of a number of temperature readings before returning a reading to a fan controller. However, even if the arithmetic mean of a series of readings is used, an outlier reading may still distort the temperature reading. For example, if a system was at a constant 50 degrees and there are 4 readings of 50 degrees and one reading of 100 degrees, the arithmetic mean would be 60 degrees, or 20% above the actual temperature. Fan speed would be increased to compensate, even though the increase was not truly necessary. A running average, where the arithmetic mean is used over a specified number of readings, would be affected even more, since the one outlier would continue to influence the running average for as long as any readings were included in the average.
Another method typically used to compensate for the inaccuracy of temperature measurements is to control the rate at which fan speed may change over a period of time, such that a sudden increase in apparent CPU temperature will not cause a sudden increase in fan speed. Slowing the change rate of fan speed may typically mitigate the effect of a sudden apparent temperature increase or decrease. However, an extreme reading will still cause a fan to ramp up or ramp down, and so it may still unnecessarily increase noise levels.
Other corresponding issues related to the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein.